Various types of vapor permeable, liquid impermeable polymeric films are known in the art. One method of making a polymeric film vapor permeable, involves mixing a matrix polymer with a substantial quantity (e.g., 10-70% by weight) of an organic or inorganic particulate filler such as, for example, calcium carbonate, and extruding a film from the blend. The matrix polymer may include a polyolefin, such as polyethylene or polypropylene, or various olefin copolymers. The film may be a monolayer film, a multilayer film which contains the filled layer as a primary layer along with thin breathable skin layers, or a multilayer film having more than one filled layer. Then, the film is heated and stretched, causing voids to form in the film.
Breathable films are employed as backsheets, or as a backsheet component laminated to a nonwoven web and/or other layers, in many of today's personal care absorbent articles, diapers being one example. Filled, stretched polyolefin films provide good water vapor transmission, making the diapers more comfortable to the wearer. As a result, the relative humidity and temperature within the diaper or other product can be reduced by using breathable films and laminates.
One drawback of the voided filled polyolefin films and laminates is that they transmit ammonia and other odor-causing vapors as well as water vapor. Ammonia is the primary odor-causing ingredient in urine, for instance. Also, the voided polyolefin films and laminates are generally not elastic to any significant extent. Also, any particle agglomerates in the film before stretching can cause large pores which will leak. Fluids which wet such films (alcohols, water with surfactants, etc.) will pass through the holes. Bacteria and viruses can pass through the holes as well. Also, the voids generated during stretching weaken the film.